Autonomous ice sheet surface mass balance measurements from cosmic rays
Autonomous ice sheet surface mass balance measurements from cosmic rays
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DOI：
10.5194/tc-12-2099-2018
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发表时间：
2018-06-19
期刊：
影响因子：
5.2
通讯作者：
Womack, Gary
中科院分区：
文献类型：
--
作者：
Howat, Ian M.;de la Pena, Santiago;Womack, Gary
由于难以获得手动测量且缺乏可靠的遥感方法，对冰川和冰盖的质量积累和净平衡的观测很少。利用宇宙射线撞击产生的快中子衰减来记录降雪水当量累积的方法是在 20 世纪 70 年代开发的，已用于大型网络积雪监测，但尚未应用于冰川和冰盖。为了评估这种潜在的方法，我们于 2016 年 4 月在格陵兰萨米特营地安装了宇宙射线中子传感装置。每小时记录中子计数大约 24 个月，并在校正大气压力和入射宇宙辐射的变化后转换为水当量厚度。对每日累积估计值进行噪声水平分析，并与手动地表核心和雪桩网络测量进行比较。基于高达 56 厘米水当量的测量，我们估计传感器的精度在水当量厚度小于 14 厘米时优于 1 毫米，在 140 厘米以下时优于 1 厘米，即大约 0.7%。我们的观察结果与表面核心测量结果一致，在各自的误差范围内，并通过与雪桩网络的比较来解释由雪漂流解释的临时偏差。我们的观察表明，日至月尺度的累积量存在很大的时间变化，但年度总量相似。基于这些结果，宇宙射线传感代表了一种潜在的变革性方法，用于获取质量积累的连续原位测量，这可能会增加气象模型和遥感对冰川和冰盖质量平衡估计的限制。
Observations of mass accumulation and net balance on glaciers and ice sheets are sparse due to the difficulty of acquiring manual measurements and the lack of a reliable remote-sensing method. The methodology for recording the water-equivalent accumulation of snowfall using the attenuation of fast neutrons generated by cosmic ray impacts was developed in the 1970s and has been employed in large-network snowpack monitoring but has yet to be applied to glaciers and ice sheets. In order to assess this potential method, we installed a cosmic ray neutron-sensing device at Summit Camp, Greenland, in April 2016. Hourly neutron count was recorded for similar to 24 months and converted to water-equivalent thickness after correcting for variability in atmospheric pressure and incoming cosmic radiation. The daily accumulation estimates are analysed for noise level and compared to manual surface core and snow stake network measurements. Based on measurements of up to 56 cm of water equivalent, we estimate the sensor's precision to be better than 1 mm for water-equivalent thicknesses less than 14 cm and better than 1 cm in up to 140 cm, or approximately 0.7 %. Our observations agree with the surface core measurements to within their respective errors, with temporary biases that are explained by snow drifting, as supported by comparison to the snow stake network. Our observations reveal large temporal variability in accumulation on daily to monthly scales, but with similar annual totals. Based on these results, cosmic ray sensing represents a potentially transformative method for acquiring continuous in situ measurements of mass accumulation that may add constraint to glacier and ice sheet mass balance estimates from meteorological models and remote sensing.